Any organic electroluminescence element (abbreviated as organic EL element hereinafter) has a charge-transporting thin film formed therein.
There are several methods of forming the charge-transporting thin film. They fall under two large categories: dry process typified by vapor deposition; and wet process typified by spin coating. The selection of an adequate method depends on the area of thin film to be formed and the solubility in organic solvents of the substance to be made into thin film.
Any organic EL element is usually provided with an anode and an emitting layer in such a way that they hold between them one layer called hole injection layer which is adjacent to the anode and one layer called hole transport layer, one over another. Such two layers allow effective charge transport, thereby causing the organic EL element to exhibit high luminance characteristics. (See Non-Patent Document 1, for example.)
On the other hand, however, these two layers usually need additional steps to be formed individually in the production process of the organic EL element.
The recent trend in the field of electronic devices is toward the simplified manufacturing process and element structure which are essential for efficient production in high yields.
One way to achieve this object is to make the functional multi-layer film which is formed in the element by lamination into a single-layer film. In this way, it is possible not only to simplify the manufacturing process but also to directly simplify the element structure. For this reason, there has arisen in various fields of electronic device a need for new materials that yield a functional single-layer film which will replace the conventional functional multi-layer film.
In the field of organic EL element, too, there is an increasing demand for new materials for a single-layer film which replaces the functional multi-layer film including of a hole injection layer and a hole transport layer, employed in the ordinary element structure.